Electric eel lights up Christmas tree

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Since the Electric Eel is not plugged in to the wall, how is it able to perform electric discharges?

The Electric Eel, Electropohorus Electricus, has special cells, electroplates, that generate an electric current. These cells are modified muscle cells that have lost the ability to contract and are specialized for the generation of electric current. E. electricus produces a signal between 500-600 V, which is powerful enough to kill other fish and possibly even an animal as large as a full grown person.

Electric organ: (Left): resting and (Right): firing Electric organ: (Left): resting and (Right): firing

The electric organs of E. electricus contain columns of stacked electroplates. One face of the electroplate is smooth and covered with nerve endings, and opposite face is deeply folded. When the electric organ is inactive, both faces of the electroplate are positive on the outside and negative on the inside. To generate electricity, the brain sends an electric signal to the first electroplate in the column. The signal opens an ion channel and lets positive sodium ions flow into the negatively charged cell. The depolarization of the electroplate surface causes a small difference in voltage across the cell, which makes the adjacent cell to depolarize as well. This generates more current and the depolarization wave passes along the electroplate column. Essentially, the stacked electroplates (up to 5000-6000 electroplates) act as a series of batteries. The charge generated from these connected "batteries" is released into the surrounding water for electrocommunication or electrolocation, or into the body of another animal to stun or kill it.

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Species description

Despite its common name, Electric Eel, the species is in the group of knifefishes, Gymnotiformes. E. electricus has an elongated, cylindrical body, typically growing to about 2 m (about 6 feet) in length, and 20 kg (about 44 pounds) in weight. It lacks caudal, dorsal and pelvic fins. The anal fin, which extends over the length of the body to the tip of the tail, controls the motion of the fish. A thick, slimy skin covers the entire body. The skin is used as a protective layer, often from the electrical current that is produced by the fish itself.

The fishes live in the muddy bottoms of rivers in the north-east of South America. E. electricus can survive in areas where the dissolved oxygen levels are reduced since they are obligate air-breathers. It rises to the surface every 10 minutes or so for gulping air before returning to the bottom. Nearly 80% of the oxygen used by the fish is taken in this way. Since the animal lives in muddy and dark waters, and is nocturnal, it relies on electricity for sensing.

E. electricus lives exclusively in fresh water since the salt in sea water has a protonic effect on the eel's charge causing it to naturally short-circuit.

Organs

The vital organs are all in the anterior portion of the body and take up only about 20 percent of the fish. The posterior portion of the body contains the electrical organs. Instead for one single electric organ, the E. electricus actually has three, Sach’s organ, Hunter’s organ and the Main electric organ. The organs are made up of electroplates, lined up as a series of batteries.

Sach's organ transmits a low signal, only about 10V in amplitude, that is used to locate prey, navigate and communicate. The Main electric organ and the Hunter’s organ are responsible for producing and storing the eel's strong electric charge (up to 500-600V). E. electricus attacks its prey by discharging its signal into the water, or more effectively, by touching the animal as it fires.

Electric eels tend to stay relatively rigid in order to fully use their electrical capabilities. They have a positive charge near the head, while the tail end is negative. When scanning their environment with electric current, they begin at the tail and finish with the head. In order to do this the fish must be able to swim backward.

Electric signal reception

In addition to producing signals, electric fish can receive and interpret electric signals either produced by themselves or by other fish. They sense electricity with a very sensitive organ called ‘electroreceptors’ which are embedded in the skin. Electroreceptors are used to detect a slight change of electric field cause by nearby objects. Electric fishes can thus electrically 'see' objects in an environment where vision is useless (at night, or in murky water) by creating an electric field and locate objects by analyzing disruptions in it.